This invention relates to an improved method of manufacture of vessels which employ multiple internal heat exchange tubes.
Historically the manufacture of vessels which employ multiple internal heat exchange tubes has presented problems of warpage due to buildup of stresses as a result of temperature differences encountered during the welding or brazing process utilized to attach the tubes to headers forming the vessel. Such warpage is a significant problem in vessels which have precoated parts particularly where the precoating material is a ceramic or porcelain material of a type which insures corrosion protection.
That is, a common practice in the manufacture of vessels is to take a tubular body and weld headers or end plates to the end of the body thereby forming an enclosed tank. The interior of the tank is then coated with a ceramic or porcelain material for corrosion protection. Subsequently, heat exchange tubes are inserted through openings in the end plates of the tank or headers. These heat exchange tubes are then welded to the headers. The welding process often causes warpage of the headers and the tube ends resulting in cracking of the protective coating. This, in turn, exposes the metal surface to corrosive activity, particularly in a water heater tank assembly.
The present invvention constitutes a method of manufacture as well as an assembly which seeks to overcome the problem of degradation of the protective coating material on the inside of a tank or vessel of the type which has multiple internal heat exchange tubes.